Not applicable.
1. Field of the Invention
The present invention generally relates to a system and method for determining the temperature to which a structure is subjected.
2. Description of the Prior Art
The temperature of a fluid surrounding an elongated probe provides important diagnostic information for structures within the fluid, e.g., in the medical field. There have been several conventional techniques for measuring such temperature, such as embedding thermister-type sensors in the probe wherein each thermister-type sensor is supported by a pair of wires. Another conventional technique utilizes fiber optic sensors based upon Bragg gratings. Bragg gratings are described in U.S. Pat. Nos. 5,493,390, 5,563,967, and 5,892,860. Bragg grating-type sensors have advantages over thermister-type sensors because fiber-optic sensors can exist on one fiber. Fiber optic sensors based on Bragg gratings sense temperature based on strain on the sensor. However, such strain also can be induced by non-temperature effects such as hydrostatic pressure, tension, bending, etc. which can cause erroneous temperature measurements. Another optional method to measure temperature makes use of Raman scattering effects. Here, light is scattered from the inhomogeneities in the glass and the scattered light is processed to determine temperature. However, it is difficult to obtain a point of measurement by this method as the spatial resolution is about xc2xd meter.
Therefore, it is an object of the present invention to provide a novel system and method for measuring the temperature of a fluid surrounding a probe wherein such system and method do not exhibit or present the problems and disadvantages of conventional techniques.
Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art in light of the ensuing description of the present invention.
In one aspect, the present invention is directed to a system for determining the temperature to which a structure is subjected, comprising an optical fiber configured for attachment to a structure, a pair of fiber sensors formed within the optical fiber, each fiber sensor being configured to have a particular coefficient of thermal expansion and particular identification, a light source for launching a broadband source of light into the optical fiber, a detector for detecting the light returning from the first and second fiber sensors, and a processor for determining the temperature to which the structure is subjected based upon the difference in the strain response of each fiber sensor due to the effects of temperature upon the fiber sensors.
In a related aspect, the present invention is directed to a method of determining the temperature to which a structure is subjected, comprising the steps of providing an optical fiber having at least one pair of fiber sensors formed therein wherein the fiber sensors are substantially collocated and each fiber sensor is configured to have a particular coefficient of thermal expansion and a particular identification, attaching the optical fiber to the structure, launching a broadband spectrum of light into the optical fiber, detecting light returning from the fiber sensors, and determining the temperature to which the structure is subjected based on the difference in strain response of the fiber sensors as a result of the effects of temperature upon the fiber sensors.
In one embodiment, each fiber sensor is configured as a Bragg grating.
In one embodiment, the identification of each fiber sensor comprises a particular fiber sensor wavelength.
In one embodiment, one of the fiber sensors comprises a coating of material that is configured to provide that fiber sensor with a first coefficient of thermal expansion and the other fiber sensor comprises a coating of material that is configured to provide that fiber sensor with a second coefficient of thermal expansion that is different than the first coefficient of thermal expansion.